The 600ex-rtii from Yongnuo is a great speedlight available for Canon users. It features built in radio communication so that you can reliably use it off camera and maintain complete control. The 600ex-rtii can be used as a master flash with other 600ex-rt’s from both Canon and Yongnuo. It can be used as a slave off camera as well when controlled by another 600ex-rt or with the YN-E3-RT controller. This speedlight also has the ability to be made to be an optically triggered slave and a slave to the built in system in many Canon cameras (infrared). It features TTL capabilities, High Speed Sync, Rear Curtain Sync, Flash Exposure Bracketing, Flash Exposure Compensation and many other useful settings. This speedlight also can be used with an external battery pack if needed. An added feature of this speedlight, as with other TTL capable speedlights from Yongnuo is the ability to use this Canon version speedlight with the Nikon wireless system as well. If you want the best that there is to offer, this is it.